Reference

Python

Debugging python

import pdb

and put pdb.set_trace() where ever break is needed -

Ubuntu and linux

Wifi connection related

First, determine the name of the WiFi interface:

nmcli d

Make sure the WiFi radio is on (which is its default state):

nmcli r wifi on

Then, list the available WiFi networks:

nmcli d wifi list

As an example, to connect to the access point 'my_wifi', you would use the following command:

nmcli d wifi connect my_wifi password <password>

Disbale sleep from SSH

sudo systemctl mask sleep.target suspend.target hibernate.target hybrid-sleep.target

and to bring it back

sudo systemctl unmask sleep.target suspend.target hibernate.target hybrid-sleep.target

Detele a nonempty directiory or folder

$sudo rm -vr folderName
-f = to ignore non-existent files, never prompt
-r = to remove directories and their contents recursively
-v = to explain what is being done

Create a new file such as python script

$ touch filename.py

To change the default bash directory, open the .bashrc file from home directory as below

nano ~/.bashrc

and then just add cd at the end. For example -

cd ~/catkin_ws/src/rpi_ros_car/src

To find command history with hint, use CTRL+R and then wirte the hint phrase,

ROS

Kill roscore

killall -9 rosmaster

Create a new catkin package

cd ~/catkin_ws/src

Now use the catkin_create_pkg script to create a new package called 'rpi-ros_car' which depends on std_msgs, roscpp, and rospy:

catkin_create_pkg rpi_ros_car std_msgs rospy 

or if you already have existing package in github, you can clone it here (see git tuorials for details). Then go to

cd ~/catkin_ws/src

and invoke

catkin_make

Before running any pythion file through rosrun, you have to make them executable as shown below -

$chmod +x mypythonscript.py

To run a executable file with rosrun under catkin workspace

$rosrun <package_name> <executable_name>

To killa rosnode if ctrl+C is not working,

rosnode kill yourNodeName

To get a list of ros node

rosnode list

Similarly, to get a list of all ros topics -

rostopic list

and to get more info about a node or topic -

rosnode info <topic name/node name>

Ros package update on Raspberry pi (if you have installed ROS on raspbian image)

mv -i kinetic-ros_comm-wet.rosinstall kinetic-ros_comm-wet.rosinstall.old
rosinstall_generator ros_comm --rosdistro kinetic --deps --wet-only --tar > kinetic-ros_comm-wet.rosinstall
diff -u kinetic-ros_comm-wet.rosinstall kinetic-ros_comm-wet.rosinstall.old
wstool merge -t src kinetic-ros_comm-wet.rosinstall
wstool update -t src

Windows Commad line

To see all connected devices in the network

arp -a

Chocolatey

Installing Chocolatey using PowerShell (with admin priviledge) -

Invoke-WebRequest https://chocolatey.org/install.ps1 -UseBasicParsing | Invoke-Expression

install package from config file for the first time -

choco install chocolatey-packages.config -y

install a software with specific version or on a specific location or getting information about a package -

choco install software_name --version -y
choco install 7zip --install-directory=P:\7z
choco info 7zip

get a list of all installed software on local drive -

choco list --local-only
choco list -li

Install multiple packages in a single command -

choco install pkg1 pkg2 pkg3 -y

Installing a package with all versions available -

choco uninstall pkg --all-versions -y

List outdated packages

choco outdated

Ignore Checksums

choco install pkg --ignore-checksums

Upgrade a Package

choco upgrade <pkg|all> [<pkg2> <pkgN>] [<options/switches>]
choco upgrade git -y
choco upgrade all -y

git

Connecting git through ssh

1. generate public and private keys through putty
2. Save private and public keys with name id_rsa (click Yes for ignoring passphrase protection)
3. make sure the saved key on PC is of OpenSSH type (use Conversion --> Export OpenSSH option)
4. Add Public key to git
5. Test connection by typing ssh -vT [email protected] on a command window.

If you are using git for the first time -

git config --global user.email "[email protected]"
git config --global user.name "Your Name"
git config --global credential.helper store

adding an existing folder to github It is always best to create a git repo on git hub first and then clone the repo on the local drive. If you are dealing with catkin packages, then before creating the package first clone the git repo and then create the package with the same name.

git pull
git add --all
git commit -m "message"
git push 

Ignore a file that is being tracked currently

git rm --cached <file>

Creating and applying stash

git stash
git stash list
git stash apply stash@{stash_index}

If you want to combine git commit and push in one command then create a make file with following commands (remember to place the make file in the smae directory where .git folder resides)

git:
	git add --ignore-errors .
	git commit -m "$m"
	git push -u origin master 

then invoke the following -

make git m="your message"

Raspberry Pi

Which version of Raspbian do I have?

cat /etc/os-release

How to modify the swap?

First turned off the swap -

sudo dphys-swapfile swapoff

Then modify the swap. As root, edit the file

sudo nano ~/etc/dphys-swapfile 

and modify the variable CONF_SWAPSIZE:1024 Save and exit. Start the swap again -

sudo dphys-swapfile swapon

Getting the right ubuntu+ROS image for Raspberry Pi 4B

It's better to use the Raspi 4B with 4gb ram As there are no standard images available for Raspberry Pi 4B + Ubuntu + ROS, I am using the image created by ubiquity robotics. https://downloads.ubiquityrobotics.com/pi.html

There might be some issues with wireless connectivity and doing ssh from PC, I will update this section once I find a way to resolve it. After flshing the image with ubiquity ubuntu image for Raspberry Pi, use the following commands one by one to make the image accessible for other robots other than ubiquity. Connect Raspberry pi to interent with cable to access ssh from PC. Find the IP address from your router page or by doing arp -a from command window. Then follow these commands -

sudo systemctl disable magni-base
sudo systemctl disable roscore
sudo pifi set-hostname NEWHOSTNAME
sudo reboot

Once it comes back live try the following -

nmcli d wifi list

If it shows all the networks nearby then -

sudo nmcli d wifi connect my_wifi password <password>

If for some reason it throws some error or does not show the wifi list on the command nmcli d wifi list, then try the following -

pifi list seen

and then

sudo pifi add MyNetwork password
sudo reboot

It might take few minutes to connect to wifi. So, emain patient and keep trying to ping.

Next, you need to free up the GPIO pins. Try,

cd /
sudo nano /etc/pifi/pifi.conf

and change the following lines -

status_led: None
button_device_name: None

save and exit. Go back to root and try

sudo nano /etc/ubiquity/robot.yaml

make sure you have the following, sonars = None and the next line with sonars = pi_sonar_v1 is commented.

sonars: None
# sonars: ‘pi_sonar_v1’

Thats it. To check core temperature of Raspberry Pi

~/opt/vc/bin/vcgencmd measure_temp

SSH

How to Connect VSCode to server through ssh for remote debugging?

1. Create SSH key (public and private) on the client PC (for example a Windows PC). There are few ways one can generate keys on Windows - using putty or openSSH.
   1. OpenSSH - Install OpenSSH for Windows. Follow the instruction given in OpenSSH for Windows. Then run sh ssh-keygen -t rsa from the Windows cmd prompt. The key will be generated and will be saved under c:/user/<username>/.ssh/.
   2. Using PuttyGen - Generate the key and save it to a location like c:/user/<username>/.ssh/. The private key for putty is called *.ppk is not compatible with OpenSSH. Therefore the private key needs to be converted into OpenSSH format. From the PuttyGen go to Conversion and select Export OpenSSH key to convert and save the private file in the desired location.
2. The public key can be copied from PuttyGen and saved in a file may be named as authorized_keys. Please note that this file does not have any extension.
3. Move the public key named authorized_keys to the server home directiory (lets say its a Ubuntu Machine) like /home/Ubuntu/.ssh/. If there is no .ssh folder exists, just create one using sh sudo mkdir /.ssh.
4. At this point of time, the client machine (like Windows) can connect to Server (Like ubuntu) without entering password. One should check it from windowd powershell or command line by using ssh username@hostname.
5. Now in VSCode, search and install the following extensions -
   1. Remote Development
   2. Remote SSH (Nightly)
6. While in VSCode, press F1 and type remote SSH to select Remote SSH: Open Configuration File. Here is an example of what I had to do to connect Raspberry Pi with VSCode. With out the full address for id_rsa (private key generated either by OpenSSH or PuttyGen) and port number, I was having some difficulties connecting to server.

   	Host rpi4ros
   	  HostName rpi4ros
   	  User ubuntu
   	  ForwardAgent yes
   	  IdentityFile C:\Users\user_name\.ssh\id_rsa
   	  Port 22

7. Press F1 again, and now try Remote SSH: Connect to Host. Now it should connect to the server without any issues.